1. Field of the Invention
The present invention relates to an active matrix type organic electroluminescent device, and more particularly, to an active matrix type organic electroluminescent device with enhanced color purity.
2. Discussion of the Background
FIG. 1 is a sectional view showing a pixel of a conventional active matrix type organic electroluminescent device. The pixel includes a thin film transistor 50 disposed in a driving area D and a display unit 60 disposed in a light-emitting area E. The thin film transistor 50 drives the display unit 60. The display unit 60 includes a first pixel electrode 61 coupled to the thin film transistor 50, a second pixel electrode 62 coupled to a power source (not shown), a light-emitting layer 87b interposed between the first and second pixel electrodes 61 and 62, and an electric charge transport layer 87a and/or 87c interposed between the light-emitting layer 87b and at least one of the first and second pixel electrodes 61 and 62.
The first pixel electrode 61 is coupled to a drain electrode of the thin film transistor 50 through a contact hole 85c formed in a passivation layer 85, which protects the thin film transistor 50 during a subsequent fabrication process. The passivation layer 85 may include a SiNx layer 85a and a SiO2 layer 85b, and the SiO2 layer 85b may be disposed on the SiNx layer 85a. 
The substrate 81 typically comprises glass and SiO2. Refractive indexes of glass and SiO2 are in the range of about 1.4-1.6, but the refractive index of SiNx is in the range of 1.8-2.0. This difference between refractive indexes may distort light emitted from the light-emitting layer 87b. FIG. 2 shows that, for the conventional organic electroluminescent device of FIG. 1, a plot between intensity and wavelength of emitted light may have a saddle-like form. In this case, the color purity of the organic electroluminescent device decreases.